Electron lens system



Patented Feb.20,1945 a ELECTRON LENS SYSTEM James Hillier, Cranbury, N. J., assignor to Radio Corporation of ware America, a corporation of Dela- Application April 1, 1943, Serial No. 481,399

5 Claims.

This invention relates to electron lens systems and particularly to improvements in magnetically -energized lenses for use in electron microscopes and analogous instruments.

'In a conventional transmission type electron microscope employing two or more pairs of lens elements or pole pieces it is customary to employ a separate source of magnetic energy for actuating each pair of pole pieces. This is a costly practice particularly when the system comprises a plurality of electro-magnets since, in such case,

separate current regulating systems must be pro vlded in the circuit to each coil.

Accordingly, the principal object of the present invention is'to provide an improved magnetically actuated electron lens system and one characterized by the economy of its parts, the simplicity of its structure, and by its trouble-free performance.

Another and important object of the present invention is to achieve the foregoing in an elec tron lens system capable of 'variabl magnification.

In the embodiment of the invention which has been selected for purposes of illustration, a single electro-magnet comprising a, coil I wound upon a hollow cylinder 2 which is constituted of a nonmagnetic material (e. g., brass) serves to actuate two pairs of apertured lens elements or pole pieces I 34 and 5-6. These separate pairs of pole pieces 3 4 and 56 may comprise the objective and projection lenses, respectively, of an electron microscope or similar instrument. They are constituted of a magnetically permeable material (e. g., soft iron) and are supported, in a manner later described, upon a hollow magnetic structure 7 which has a sliding fit within the bore of the non-magnetic cylinder .2 so that the magnification of the instrument may be varied by moving the entire lens assembly axially within the said cylinder and with respect to anexternally mounted specimen holder 8. The coil or magnet l is coupled, magnetically, to the outer pole pieces ,3

and '6 by a soft iron shell comprising an'outen cylinder ,9 and a pair of apertured end plates l0 and II, respectively. Thus, the magnetic flux which is applied to the outer pole piece 3 through the end plate I 0 permeates the space between the objective lens elements 3 and 4. The magnetic circuit back to the sourc I from the inner pole piece '4 is completed through a path which'ineludes the slidable magnetic structure I. the projection lens elements 5 and 6, the opposite end plate I l, and the outer cylinder 9.

The electron lens system of the present invensembled and disassembleche. g., for purposes of inspection and. adjustment. To this end, each of the outer pole pieces is threaded, as indicated at 3a, 6a, throughout at least a portion of its length and is attached to the slidable magnetic structure I by means of complementarily threaded nonmagnetic sleeve or nipple l2 or l3, respectively. One of the outer pole pieces, in this case the piece 6, is provided with a threaded hub portion 6b,and

this hub has a knob to thereon. The knob 60,

when turned, serves to advance or to retract the entire pole piece assembly with respect to the fixed specimen holder'B. Access may be had to the interior of the central magnetic member 1 by. unscrewing the inner pole pieces '4 and 5 which are threaded on the opposite ends of the said member.

From the foregoing it is apparent that the present invention provides an improved magnetically actuated electron-lens system capable of variable magnification, and one characterized by the economy of its parts, the simplicity of its structure, and by its trouble-free performance.

What is claimed is: i

1. A magnetically actuated electron lens system including, in combination, a hollow cylinder constituted of a non-magnetic material, mounted adjacent to the outer surface of said cylinder for creating a magnetic field about said cylinden. a plurality of pairs of pole pieces mounted in spaced axial alignment within the magnetic ,field about said cylinder, means for magnetically coupling one pole piece of each pair to said field creating means, and means within said cylinder for completing the magnetic circuit between said field creating means and the other pole piece of each pair.

2. The invention as set forth in claim 1 and wherein said means for creating said magnetic field comprises a single electro-magnet.

' 3. A magnetically actuated electron lens system including, in combination, a hollow cylinder constituted of a non-magnetic material, a singl coil for establishing a magnetic field mounted. adjacent to the outer surface of said cylinder, a magnetic structure comprising an outer cylinder and a pair of oppositely located apertured endplates mounted about said coil with the apertures in said end-plates in alignment with the bore of said innercylinder, a plurality of pairs of spaced apart pole pieces mounted along a common axiswithin said magnetic cylinder with the-outer pole pieces of each pair in contact, respectively, with one of said apertured end plates, a magnetic memtion isso constructed that it may be easily as- 65 her mounted for axial movement within said nonmeans magnetic cylinder and upon which said pole pieces are supported, and means for moving said magnetic member and, hence, said pole pieces simultaneously along said axis with said outer pole pieces in contact with said end-plates.

4. The invention as set forth in claim 3 and wherein the inner pole piece of each pair is removably aflixed to said magnetic member and the outer pole piece of each pair is removably affixed 5. A magnetically actuated lens system comprising a plurality of pairs of agertured pole pieces mounted in spaced array along a common axis, a single magnet in the form of a cylinder disposed about said axis in the space between said pole pieces for subjecting said pole pieces to a magnetic field, and means for relatively moving said pole pieces along said axi within said magnetic field and with respect to said magnet, Whereto its adjacent inner pole piece by means of a non- 10 by to vary the magnification of said lens system.

magnetic element.

JAMES HILLIER. 

